Knowledge

RPC_S_UNKNOWN_AUTHN_LEVEL - 1748 (0x6D4)

The authentication level is unknown.

Updated: Feb 21, 2026

Overview

The error code RPC_S_UNKNOWN_AUTHN_LEVEL (1748, 0x6D4) is encountered during Remote Procedure Call (RPC) operations when an unknown or unsupported authentication level is detected. This error indicates a failure in the security context of the RPC operation.

Technical Background

Remote Procedure Calls are used to invoke functions on a remote computer as if they were local. Security levels define the type and strength of authentication required for an RPC call, ensuring that only authorized clients can access specific services or resources.

Error Details

  • Error Name: RPC_S_UNKNOWN_AUTHN_LEVEL
  • Numeric Code: 1748 (0x6D4)
  • Short Description: Indicates the detection of an unknown authentication level during an RPC operation.

Common Causes

This error typically arises due to one or more of the following issues:

  • Incorrect Authentication Level: The client or server may have specified an unsupported or unrecognized authentication level for the RPC call.
  • Configuration Mismatch: There might be a mismatch in security settings between the client and server configurations, leading to an unknown authentication level being detected.

Real-World Context

This error can occur in various scenarios where RPC operations are used, such as network services, distributed applications, or inter-process communication (IPC) mechanisms. It is particularly relevant in environments with complex security policies or when integrating different systems that use varying authentication levels.

Is This Error Critical?

The criticality of this error depends on the context and the specific application using RPC calls. In general, it indicates a potential security issue and should be addressed to ensure proper operation and security compliance.

How to Diagnose

To diagnose the cause of RPC_S_UNKNOWN_AUTHN_LEVEL, follow these steps:

  1. Review Operation Context: Ensure that the authentication level specified in the RPC call is supported by both the client and server configurations.
  2. Validate Parameters: Check the parameters passed during the RPC operation to ensure they are correctly configured for the required security level.
  3. Confirm Object Types: Verify that the objects involved in the RPC operation (e.g., services, endpoints) have consistent authentication requirements.
  4. Verify Input Data: Ensure that all input data is valid and conforms to expected security policies.
  5. Check Limits or Constraints: Confirm that there are no system limits or constraints preventing the use of a specific authentication level.

How to Resolve

To resolve this error, consider the following actions:

  • Correct Parameter Usage: Ensure that all parameters used in RPC calls are correctly configured for the required security level.
  • Adjust Operation Context: Modify the operation context if necessary to align with supported authentication levels.
  • Restore Data: If data corruption is suspected, restore or reconfigure the relevant security settings.
  • Retry Operation with Valid Inputs: Attempt to perform the RPC operation again with valid and correctly configured inputs.

Developer Notes

Developers should be aware that this error can impact the reliability and security of distributed applications. Proper configuration and validation of authentication levels are crucial for avoiding such errors.

Related Errors

  • RPC_S_AUTHN_LEVEL_NOT_SUPPORTED
  • RPC_S_CANT_ACCESS_DOMAIN_INFO
  • RPC_S_CALL_FAILED_DUE_TOfdfd

FAQ

Q: What does the RPC_S_UNKNOWN_AUTHN_LEVEL error mean?

A: This error indicates that an unknown or unsupported authentication level was encountered during an RPC operation.

Q: How can I prevent this error from occurring?

A: Ensure consistent security configurations between client and server, validate all parameters for correct usage, and verify the supported authentication levels in your environment.

Summary

The RPC_S_UNKNOWN_AUTHN_LEVEL error is a specific indication of an unsupported or unrecognized authentication level during RPC operations. Addressing this issue involves reviewing operation context, validating parameters, confirming object types, and ensuring consistent security configurations.